Dinosaur Footprint Asemblage from the Lower Cretaceous Khok Kruat Formation, Khorat Group, Northeastern Thailand

Accepted Manuscript Dinosaur footprint asemblage from the lower Cretaceous Khok Kruat Formation, Khorat Group, northeastern Thailand Shohei Kozu, Apsorn Sardsud, Doungrutai Saesaengseerung, Cherdchan Pothichaiya, Sachiko Agematsu, Katsuo Sashida PII: S1674-9871(17)30032-4 DOI: 10.1016/j.gsf.2017.02.003 Reference: GSF 539 To appear in: Geoscience Frontiers Received Date: 30 November 2016 Revised Date: 19 January 2017 Accepted Date: 3 February 2017 Please cite this article as: Kozu, S., Sardsud, A., Saesaengseerung, D., Pothichaiya, C., Agematsu, S., Sashida, K., Dinosaur footprint asemblage from the lower Cretaceous Khok Kruat Formation, Khorat Group, northeastern Thailand, Geoscience Frontiers (2017), doi: 10.1016/j.gsf.2017.02.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT MANUSCRIPT ACCEPTED ACCEPTED MANUSCRIPT Dinosaur footprint asemblage from the lower Cretaceous Khok Kruat Formation, Khorat Group, northeastern Thailand Shohei Kozu a, *, Apsorn Sardsud b, Doungrutai Saesaengseerung b, Cherdchan Pothichaiya b, Sachiko Agematsu a, Katsuo Sashida a a Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan b Department of Mineral Resources, Ministry of Natural Resources and Environment, Thailand MANUSCRIPT Corresponding author. E-mail address: [email protected], Tel: +81-29-853-6138 ACCEPTED 1 ACCEPTED MANUSCRIPT Abstract The Khok Kruat Formation is the upper part of the Khorat Group, which consists of upper Lower Cretaceous non-marine sedimentary rocks in northeastern Thailand. Many dinosaur footprints have been known from the upper Lower Cretaceous (Aptian–Albian) Khok Kruat Formation at the Huai Dam Chum (Tha Uthen) site, northeastern Thailand. Approximately 600 tracks occur in thin mudstone layer of the northern part of the outcrop at the Huai Dam Chum track site. Two types of footprints, small-sized theropod and crocodylomorph are imprinted with mud cracks and ripple marks on the thin mud layer. Most of footprints are referred to cf. Asianopodus , and are imprinted by small-sized MANUSCRIPT theropoda, probably ornithomimosauria. Theropod tracks are mainly separated into two groups, Group A and Group B. From ichnological viewpoints, the small-sized theropod track assemblage indicates the herd behaviour and its idiosyncratic group composition. In particular, the histogram of size-frequency measurements of Group A shows the anomalous bimodal distribution. We consider that there are two hypotheses; the first one is due to the male-female difference,ACCEPTED and the second is a result of the different growing stage. Keywords: Dinosaur footprint assemblage; Cretaceous; Khorat Group; Khok Kruat Formation; Thailand 2 ACCEPTED MANUSCRIPT 1. Introduction Gregarious behaviour has been suggested for a number of dinosaur taxa, including ceratopsids, ornithopods, theropods, and sauropods (Myers and Fiorillo, 2009). Such behaviour is known from multiple examples of skeletal evidence and from abundant footprint evidence (Gillette and Lockley, 1989; Lockley, 1991). However, at present, most of the firm evidence of gregarious behaviour is provided by the ichnological record, with many tracksites exhibiting signs of group behaviour (table 1 in García-Ortiz and Pérez-Lorente, 2014). The footprint record provides a great deal of information about the MANUSCRIPT herds of imprint producers that is not available in the bone fossil record, including movement speed, style of gregarious behaviour, herd structure, and the organigram within a group (e.g. Gillette and Lockley, 1989; Lockley, 1991). Gregarious behaviour has been confirmed in sauropod track assemblages (e.g. Lockley et al., 1994, 2012) and ornithopod track assemblages (e.g. Ostrom, 1972; Currie, 1983; Fiorillo et al., 2014). Similarly, gregarious behaviourACCEPTED was common in small bipedal dinosaurs (Lockley and Matsukawa, 1999). 3 ACCEPTED MANUSCRIPT The Upper Triassic to Lower Cretaceous Khorat Group, which consists of non-marine sedimentary rocks, crops out widely in northeastern Thailand (Fig. 1). Many fossils such as dinosaur bones, dinosaur footprints, fish, crocodilians, turtles, bivalves, and palynomorphs have been recovered from the Khorat Group (Fig. 2) (Meesook, 2011; Meesook and Saengsrichan, 2011). At the Huai Dam Chum dinosaur tracksite, which is located on the eastern edge of northeastern Thailand, a number of dinosaur tracks formed by small-sized bipedal dinosaurs are present in outcrop. Dinosaur footprints have previously been reported from this area (Buffetaut et al., 2005; Le Loeuff et al., 2005, 2009; Sato and Tumpeesuwan, 2005; Matsukawa et al., 2006); however, there has been no previous study of the MANUSCRIPT ichnotaxonomic classification or quantitative commu nity analysis of the dinosaur footprint assemblage. In this study, we systematically describe tracks and conduct quantitative analysis of theropod tracks from the upper Lower Cretaceous Khok Kruat Formation of northeastern Thailand. ACCEPTED 2. Geological setting 4 ACCEPTED MANUSCRIPT The Upper Triassic to Lower Cretaceous non-marine sedimentary rocks exposed in northeastern Thailand are referred to as the Khorat Group (Ward and Bunnag, 1964). Buffetaut et al. (1993) subdivided this group into eight formations, which are (from oldest to youngest) the Huai Hin Lat, Nam Phong, Phu Kradung, Phra Wihan, Sao Khua, Phu Phan, Khok Kruat, and Maha Sarakham formations (Fig. 2). However, there is still considerable debate about the age, internal stratigraphic relationships, and depositional environment of the group (e.g. Racey et al., 1994). The Khorat Group has yielded many dinosaur bone fossils; footprints have also been reported from several areas such as Phu Faek and Tha Uthen on the Khorat Plateau (e.g. Le MANUSCRIPT Loeuff et al., 2005, 2009). Knowledge of the East Asian dinosaur fauna has been improved by these studies. Dinosaur footprints at the Phu Luang site were first reported by Buffetaut et al. (1985a); this pioneering work was followed by many studies of dinosaur ichnology in northeastern Thailand (e.g. Buffetaut et al., 1985b, 1997, 2005; Buffetaut and Suteethorn, 1993; Polahan and Daoperk, 1993; Le Loeuff et al., 2002, 2003, 2005, 2007, 2008, 2009; Lockley et al., 2002,ACCEPTED 2006b, 2009). The Khok Kruat Formation, which is one of the upper units of the Khorat Group, is widely distributed in the foothills of the Phu Phan Range. In general, the formation consists 5 ACCEPTED MANUSCRIPT of fluvial deposits of mainly reddish-brown fine- to medium-grained sandstone, conglomerate, siltstone, and mudstone (Meesook, 2011). The Khok Kruat Formation is conformably underlain by the Phu Phan Formation and is unconformably overlain by the Maha Sarakham Formation. The fresh-water shark Thaiodus ruchae has been recovered from the Khok Kruat Formation and also from the Takena Formation of the Lhasa block of Tibet, the latter having been dated as Aptian–Albian on the basis of foraminiferal fossils (Cappetta et al., 1990). From borehole samples, Sattayarak et al. (1991) suggested an Aptian age for the upper part of the Khok Kruat Formation (Racey and Goodall, 2009). Meesook (2011) indicated that the depositional environment of these rocks was MANUSCRIPT meandering rivers, although less mature than the rivers that deposited the Sao Khua Formation. 3. Occurrence of tracks ACCEPTED The tracks described herein are preserved at the Huai Dam Chum site (N17°71'30.01", E104°38'15.76"), Ban Lao Nat, Tha Uthen District, Nakhon Phanom Province, northeastern 6 ACCEPTED MANUSCRIPT Thailand (Fig. 1). The Khok Kruat Formation crops out at the Huai Dam Chum site (e.g. Le Loeuff et al., 2003). The outcrop, which consists mainly of very-fine-grained sandstone, is exposed along route 212 (Fig. 3A). Footprints are imprinted on the upper surface of a thin mudstone layer. The succession at this site (Fig. 4) consists of pinkish-brown sandstone with parallel laminations (~25 cm thick) overlying the footprint-bearing thin mudstone layer, which contains mud cracks and ripple marks. Pinkish-brown fine-grained sandstones with cross-laminations (5–15 cm thick) and pinkish-brown fine-grained sandstones with wavy-parallel laminations (15–25 cm thick) are observed in the lower part of the section. Reddish-brown fine-grained sandstone, with parallel laminations in its lower part and MANUSCRIPT wavy-parallel laminations in its upper part (~65 cm thick in total), is underlain by pinkish-brown fine-grained sandstone (~30 cm thick) in the middle part of the section. In the upper part of the section, pinkish-brown fine-grained sandstone with wavy-parallel laminations, often discontinuous, is intercalated with white medium-grained sandstone with wavy-parallel laminations (10–15 cm thick). The stratigraphically uppermost part of the section consistsACCEPTED of pinkish-brown fine-grained sandstone (~60 cm thick). On the footprint-bearing thin mudstone layer, current-ripple marks that show a NW flow direction and mud cracks are overprinted by footprints (Figs. 5 and 6). 7 ACCEPTED MANUSCRIPT The footprint-bearing outcrops are covered by an artificial roof for

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